With Carkeek, the team keyed into the considerable development work, design and affirmation loops done over previous iterations of his 40s, dating back to the HPR40 Spookie for American Steve Benjamin, and before that to the GP42s he designed alongside Marcelino Botin. To build a quick Fast40+, the primary challenge is similar to a TP52: reducing and lowering weight in the boat while maximizing its righting moment. The rules and resulting solutions differ greatly between the two classes, however. The TP52 is a highly defined box rule, whereas the Fast40+ is an open box, relying heavily on IRC. Take weight, for example: The TP52 rule specifies a minimum limit (plus vertical center of gravity limitations on the mast, etc.), whereas the Fast40+ has no defined minimum. Instead, Fast40s must have an IRC displacement-to-length ratio of less than 110 (less than 90 for new boats) and an IRC TCC of 1.21 to 1.27. The TP52 rule includes a maximum bulb weight, whereas designers have found IRC’s sweet spot for Fast40+ bulbs at around 2,000 kilograms. Where there is much greater variation among Fast40s is in fin weight and vertical center of gravity.